29 February, 2008

Genesis, Exodus, Leviticus, Numbers and Deuteronomy form the first five books of the Bible. They are known collectively as the Torah, and also as the Pentateuch, and as the Five Books of Moses. Traditionally they were said to have been written by Moses himself and include creation accounts, folk tales, ancestry listings, place name etymologies and many, many laws and codes of behaviour. It is clear to anyone who reads the books that they cannot have been written by Moses himself. Deuteronomy 34 includes some accounts of Moses’ death and includes phrases like “And no man knows his burial place to this day” and “And a prophet did not rise again in Israel like Moses”. So either Moses was ghost writing much later, or he was writing about his upcoming death. Neither of these makes as much sense as the idea that some other author was writing these lines. But who was this author?

This question was asked in the nineteenth century and from careful study of the text a theory grew up which is now called the Documentary Hypothesis. The basic idea is that the Torah we have today (and indeed have had for over two thousand years, it hasn’t changed much since the earliest versions we have) is composed of various documents that were spliced together by editors (redactors). These source documents could be isolated within the text by following clues within the text. Much of the bible seems contradictory, but this is only because it is, in fact, contradictory. By looking through the text it was possible to see that these contradictions went hand in hand with each other, and that if the text is peeled apart and broken into different strata, each layer of text works as a coherent whole.

The four main documents that make up the Torah are designated J, P, E and D (There is also JRE, Dtr1, Dtr2 and R, but we can leave those aside for now). In the J stories, God is always called Yahweh (Jahwe in German , hence J source). Yahweh is anthropomorphic, will chat to humans and is full of mercy. In the E stories God is called El, or Elohim, until his name is revealed to be Yahweh to Moses. In the P stories (the priestly source), much is made of the Aaronite priesthood. God is depicted as being Just rather than merciful. The only way to get into God’s good graces in the P stories is by bringing sacrifices to the priests. The D stories take up most of Deuteronomy and are mainly law codes with a framing story about Moses.

There are various clues within the text which show which of the source documents any particular part of the Torah came from. What is amazing to see is how much of the inconsistency disappears when each of these sources is read on its own. The time of writing can also be roughly placed. J was writing sometime before the 7th century BCE, as was E. The P and D sources were written later, and all four were before the Babylonian exile of 586 BCE (with later editing making up a small part of these books). By looking carefully and critically at these books, and seeing where the different sources place their emphasis we can get a glimpse of the early disagreements within the Hebrew community. Just as with early Christianity there is a wealth of difference visible in the texts we still have, indicating that the ideas of Judaism were varied and rich and not as narrow as some would have us believe.

Moses didn’t write the first five books of the bible. Nor did any one single person. The Documentary Hypothesis sheds light on the origins of the bible and also saves us from having to posit a schizophrenic as it’s author.

24 February, 2008

Looking back to the past, scientists have narrowed down the age of the universe, the age of the earth and how long ago life started. Current estimates put the beginning of the universe at about 13.7 billion years ago. The Earth formed along with the rest of the solar system about 4.6 billion years ago. There is evidence that there was life on Earth about 3.8 billion years ago, and there are fossils from 3.5 billion years ago which are visible to the naked eye. These fossils are stromatolites, large mats of bacteria. At this time there was no multicellular life, but these large groups of bacteria stuck close together as they multiplied and formed mounds that were up to 30cm wide. They lived in the shallow seas, gathering energy from the sun. At this time there was no thick ozone layer to protect life from ultraviolet radiation and so life tended to stick to the oceans. Since the sun was a good source of energy a lot of life hugged the shallow coasts of the continents where the benefits of the sun could be had while the water protected the vulnerable life from the more harmful radiation.

Life at this time was not as complex as it is now. The cell is rightly seen as a marvel of chemistry, a miniature factory that cannot have evolved in any small amount of time. Indeed it did not evolve overnight, and though it is unclear exactly when very complex cells and multicellular life first arose, it is not until the Vendian Period, 620 million years ago, that there is any evidence of multicellular life in the fossil record. So from the beginning of life, it took over 3 billion years before there were complex creatures that could perhaps be called animals. Even here the animals were more like jellyfish and worms, with no hard parts like shells or bones. They finds of fossils from this period indicate that they were made of harder material than jellyfish today, but even so the seas of this time would have no fish, no squid, no swimming creatures that hunt or hide. The land above would perhaps have some bacteria on it, but nothing would walk the surface and nothing flew in the air. No insects or birds would disturb a traveller to this time.

Once multicellular life had gotten a hold it wasn’t long before it developed some amazing specialisation. By being able to have specific cells for specific functions, and also by introducing sex for the first time, evolution and natural selection took off. The Cambrian explosion is the term used to describe the appearance of a huge amount of new species in the fossil record about 540 million years ago. Many of the body forms of major groups of creatures today can be seen in their ancient form in the fossils from this time. Also by this time the oxygen content of the atmosphere had risen from practically nothing 3 billion years before to something near it’s present level. This oxygen interacted with solar radiation to create ozone which allowed creatures to live out of the oceans for the first time. And here on land life began to thrive.

It took the vast majority of the time that the Earth has existed to get to this stage. In those 3 billion years the groundwork had been laid that would allow the colonisation of almost every part of the planet by life. If you were to randomly time travel to some part of the Earth’s history, not only is it extremely unlikely that you would meet another human, it’s also quite unlikely you would meet a mammal or even any animal at all. We multicellular beings are fairly recent additions to the planet but through our use of complex bodies, and the power of sex in creating new variation, we have come a long way in a mere 500 million years.

20 February, 2008

El, the High God, was upset. He was strolling along with Noah, a most virtuous man, and saw that the world had become corrupted. It wasn’t clear what has caused this corruption but nonetheless El decided to destroy all of the living things since it had worked so well for some of the other Gods. He did have a thing for the unblemished Noah though, and thought he would spare this mortal. El gave Noah detailed instructions on how to build the Ark, how many cubits in length it should be (300), what wood to make it out of (gopher wood), how many people to bring (himself, his wife, his sons and their wives), how many animals to bring (two of each, male and female), how much food to bring (enough for everyone for an unspecified time), how many bathrooms to have (none, like the starship Enterprise), how much to charge at the breakfast bar (50 shekels, it’s a seller’s market), what colour to paint it (light blue) and how much to pay the contractors who did all the work (it didn’t matter, they’d all be dead soon enough).

All the animals and birds came, two by two, into the Ark. Seven days later El split open the fountains of the Deep, and opened the doors in the sky, and the waters flooded in. For forty days and forty nights it rained, and the waters grew strong. All the people and animals and birds died in the flood. After a hundred and fifty days El wondered why it was so quiet and suddenly remembered his favourite Noah. El ate some fibrous nourishment and then passed a wind over the Earth so that the waters decreased. He closed the fountains of the Deep and the trapdoors in the sky. Five months after the start of the destruction the Ark came to rest on the mountains of Ararat. The water kept receding, and three months later the tops of the mountains appeared. Noah let a raven go and it went back and forth until the water dried up. Nevermore would the raven return to Noah. Finally, a year after the start of the flood, the Earth was again dry and El told Noah to leave the Ark, since Noah couldn’t do anything without El’s say so, even though he knew it was safe from the whole raven incident a few months before.

The bewildered animals, birds and humans stepped out onto this newly devastated world and gave thanks to El for not killing every living thing. El said to Noah, “Be fruitful and multiply. I give you dominion over all living things, you can eat what you want as long as you don’t eat the blood. Oh, and if any human kills any other human then they shall be put to death since they killed something in my image. Let’s see, what else…”

“Oh mighty El, ” inquired Noah, “how can we be sure that you wont try to kill us all again with another flood? Or if you don’t, what about another of the Gods, because I’ve heard a lot of stories about how this sort of thing keeps happening.”

“Tell you what little favoured mortal, I shall establish a covenant with you and with all the creatures of the earth. I will put my rainbow in the clouds and whenever I, or anyone else, tries to flood the world we shall see the rainbow, and it will remind us of you and your campy ways. Thus we shall never again try to flood the world. It’s useful to have little reminders like that I find.”

And so the might El, king of all the Gods, finally managed to stop everyone from trying to flood the entire Earth.

18 February, 2008

Gamma Rays lie at the far end of the electromagnetic spectrum. The most energetic form of light, Gamma Rays have the shortest wavelength. Electromagnetic radiation (light) has different properties depending on how much energy it has. This energy is directly related to the wavelength, so light with an extremely long wavelength (like Radio) does not have much energy in each photon. At the other end of the spectrum, gamma rays have very short wavelengths and a huge amount of energy in each and every photon. This energy can be very dangerous to living cells, and unlike the Hulk you are more likely to end up with cancer than super powers by being exposed to a lot of gamma radiation. In fact Gamma Rays are used to irradiate medical tools to ensure they have no leftover bacteria after an operation. Gamma Rays have limited uses on Earth, and we certainly wouldn’t want a mass explosion of them. In the late 1960’s, massive gamma ray bursts were detected which, if close enough, would wipe out all life on the planet.

In 1963 the Partial Test Ban Treaty came into effect. The Treaty banned setting off nuclear explosions in space, and the United States launched several satellites in order to monitor the Earth and watch for any illegal explosions. By the end of the decade they had not detected any radiation from the Earth’s atmosphere to suggest illegal weapons were being tested, but they had detected gamma rays coming from deep space. Later space missions also detected these bursts, but due to low resolution could not pinpoint where they came from. Just a decade ago, the BeppoSAX mission finally allowed scientists to discover the origin of these gamma ray bursts (GRBs). It was clear that these massive explosions were extra galactic in nature, and came from a long, long time ago. The current best accepted theory is that these GRBs are caused when an extremely massive, rapidly rotating star falls into a black hole. The energy released is immense.

If such a burst was to happen within 100 light years of the Earth it would blow the atmosphere away and melt the surface of the planet. Although only half of the Earth would be hit by the burst it would still manage to wipe out most, if not all, of life. Even at a several thousand light years away a GRB would cause mass extinction on the Earth. It is extremely unlikely that any such burst will occur near us, all of the really high energy GRBs occur far, far in the past, and possibly could only occur in the conditions of the early universe. Still, it would be a good idea to stay away from a star falling into a black hole. You wouldn’t like them when they’re angry.

15 February, 2008

Yahweh the storm God was upset. The humans had produced many fine women and the Sons of El, the high God, had descended from the sky to enjoy the delights of their flesh. These human women were very attractive to the Gods, mainly because they were the first females they had encountered that they weren’t related to. And so they frolicked, and played, and had fun, and due to having no contraception gave birth to the Nephilim, demigod heroes of renown. These heroes made a lot of noise and engaged in a lot of activity of dubious moral character. Much later people would think these Nephilim were hybrid space aliens, but this tale was long before that came fashionable. Yahweh looked down from the sky at what humanity had become, and he grieved. Their evil was filling the world, and quicker than he imagined possible thanks to the Sons of El and the Nephilim.

“I’ll wipe out these humans from the face of the earth because I regret that I made them.” With a tear in his eye he prepared to whip up a storm. Just then he saw Noah, one of Yahweh’s favourites. “Quickly, ” he said to Noah, “all of your household, get into an ark. And bring 7 pairs of every pure animal, you’ll need them later, and one pair of all the others. Bring the flying birds too.”

Noah did as Yahweh commanded, he brought everyone into the Ark, and Yahweh closed it for him. The flood came upon the earth for forty days, and the waters covered even the highest of mountains. All the animals on the ground died. Even the birds of the air died, the poor sparrow, and eagle, and hawk. Ducks survived of course and floated alongside the ark taunting their non-aquatic brethren. Then the rain was restrained and the flood waters went back from the earth. Noah opened a window and let go a dove which could not find a resting place and so returned. He waited a week and let it go again, and this time it returned with an olive branch in its mouth, and Noah was pleased. Noah hoped that a dove with an olive branch would become some sort of sign of peace after any maniacal genocide had happened. Finally after another week he released the dove again and it didn’t come back. It had either found land or just didn’t want the company of Noah any more and figured a slow lingering death was preferable to talking to the future father of humanity.

Eventually the ark came to rest on land and Noah built an alter to Yahweh. He took some of the pure animals and some of the pure birds of the air and offered sacrifices on the alter. And Yahweh smelled the pleasant smell and said “You know something, you humans are inclined to evil from when you’re young, and it’s not really your fault. Tell you what, I wont try kill all of you again in one big shot. I’ll just kill you in little doses.”

“Thank you oh mighty Yahweh!” said Noah, “and what about giving me the OK to be fruitful and multiply? And maybe show us a rainbow?”

“You’re probably thinking of another flood story to do with El.” said Yahweh. “After all, just because I have promised never again to kill everyone, doesn’t mean that some other God wont try to do just that…”

13 February, 2008

Antimatter is often misunderstood. One common misconception is that if a small piece of antimatter ever connects with normal matter then there will be a chain reaction and huge amounts of death and destruction will follow. Another is that there exist antimatter versions of ourselves somewhere out in the universe who have goatees and are irredeemably evil. Neither of these have been shown to be true, but antimatter does have some nice properties.

In essence, antimatter is like normal matter except that some of its properties are reversed. Only some though. Antimatter has positive mass for instance, and can act much like normal matter. The most obvious change is that antimatter has the opposite charge from normal matter. So a proton has positive charge and an anti-proton has negative charge. Similarly an electron has a negative charge and an anti-election (called a positron) has a positive charge. When matter and anti-matter meet they do indeed annihilate each other completely leaving a lot of energy behind. There is no anti-energy so we can detect these matter/antimatter interactions in the same way as any other energy burst.

In the centre of our galaxy there is a large cloud of antimatter. Large as in 10 000 light years across, this is a big chuck of the milky way. It was discovered in the 1970’s when high flying balloons equipped with gamma ray detectors managed to discover a lot of energy coming from the centre of the milky way. The gamma rays all had the same energy level, 511 keV, which is the energy level emitted when a positron and electron collide. For a long time it wasn’t clear what was creating this cloud of positrons, until recently when the area of the cloud was mapped rather precisely onto an area where there are a special form of binary star system. The systems have a low mass star circling a black hole or neutron star. In these systems the low mass star is slowly being eaten by its more massive companion and in some way, not yet fully understood, the interaction is belching out positrons at an incredible rate. Some of the mystery of the antimatter cloud has been solved, but more remains to be discovered.

And in fact we use positrons here on Earth. Positron emission tomography is a way of seeing processes inside people (and animals) without cutting them open. A radioactive substance is introduced into the body, and when it decays into a more stable atom a positron is emitted. This positron then collides with a nearby electron and gamma radiation shoots off in opposite directions at 511 keV. By detecting these two bursts of radiation it’s possible to map where the radioactive substance ended up. This is used to diagnose and monitor various cancers for instance, and is also used when developing new drugs in animals. By using PET scans you can follow the course of where a treatment drug goes without dissecting the test animal.

Even without going for a PET scan you will still manage to encounter antimatter. Just as millions of normal neutrinos (very small elemental particles) pass through your body ever second, so too do antimatter neutrinos whizz happily through you. And these anti-neutrinos neither cause a massive chain reaction which will destroy the world, nor do they cause people to grow goatees and become evil. Well, not that often anyway.

8 February, 2008

Far from Earth, orbiting the furthest major planet from the Sun , there is a very cold, very odd moon. The planet Neptune was discovered in 1846 and the moon Triton was discovered only two weeks later. For a long time it was known just as Neptune’s satellite, it would take over a hundred years for the next moon to be discovered orbiting this distant world. Triton is a big moon, the seventh largest in the solar system, roughly the same size as Earth’s moon. But unlike the other large moons Triton goes the wrong way around its parent planet.

Most moons seem quite happy to trundle around their planet in the same direction as their planet spins. This is thought to be because the moons formed at the same time as the planet, and Triton’s orbit around Neptune indicates that it is an intruder into the Neptunian system. Evidence of this has been seen with the Voyager space probe and the Hubble telescope. The front part of Triton, the leading part as it sweeps through its orbit, is heavily cratered. When Triton first arrived at Neptune it seems to have swept up much of the orbiting debris, and since it was going in the opposite direction the collisions were that much nastier. These head on collisions have caused one half of Triton to bear the marks of its entry into the space around Neptune.

Triton has other interesting characteristics too. It has a faint atmosphere. It has cryovulcanism, nitrogen geysers, rift valleys and a large polar cap. Since Triton was only visited once during a brief flyby, we only limited close up information on it. But one thing we do know is the eventual fate of this backwards moon. Unlike our moon which is slowly moving further from the Earth, Triton is inexorably being pulled towards Neptune. Its retrograde motion has sealed its fate. It will take a few billion years, but Triton will eventually get too close to Neptune. When it does the moon will be subject to large gravitational forces that will overcome its own and the moon will begin to break up. The tidal forces will shatter Triton into an immense number of smaller and smaller particles until it will likely become a ring of moonlets. And unlike the tiny rings that circle Neptune just now, this ring will be spectacular. Triton is made of bright ice, and this reflective substance will be much more visible. The sheer size of Triton will also mean that the rings will be suitably impressive, possibly larger than those of Saturn.

Triton has barged its way into orbit around Neptune. It has suffered collisions and will eventually be ripped apart. But in it’s death it will at least look fantastic.